Microtubule-associated protein 2 (MAP 2), a high MW protein found abundantly in neural tissue, has received increasing attention as a putative structural link between two major fibrous organelles of the neuron, neurofilaments (NF) and microtubules. We have recently generated experimental data indicating that MAP 2 may have an important role in certain forms of pathological reorganization of the neuronal cytoskeleton, vis., Alzheimer-type neurofibrillary degeneration and certain experimental models of neurofilamentous pathology. While MAP 2 usually occurs as a sidearm of microtubules, we have produced AlphaMAP 2 monoclonal antibodies and used them to show that MAP 2 segregates with NF collections that are devoid of microtubules in aluminum neurotoxicity and in Alzheimer neurofibrillary tangles (NFT). Other workers have recently reported similar findings in the neuronal intoxications induced by IDPN (2) and vinblastine (40). The central purpose of this proposal is to carry out protein chemical characterization of the MAP 2 protein and to study its role in model systems of neurofilamentous reorganization and in human NFT in Alzheimer's disease. Biochemical characterization will employ the three monoclonal antibodies we have produced to different MAP 2 epitopes. One of these epitopes is abundantly present in NFT. The other epitopes cannot be detected in NFT and therefore may have been modified or omitted during the formation of NFT. Primary sequence analysis of MAP 2 immunoreactive fragments that contain the epitopes recognized by our various monoclonal antibodies will shed light on how MAP 2 undergoes molecular reorganization, along with NF and perhaps other proteins, to form NFT. The hypothesis that the function of the MAP 2 sidearm on microtubules is to interact with NF will be approached by determining the amino acid composition of the molecule and its various functional domains. NF are thought to have charged sidearms probably made up of repeating residues that could serve as a scaffolding for interactions with other proteins (82). Discovery of a comparable domain in MAP 2, for example, might suggest that the nature of the interaction between these proteins is electrostatic. The nature of MAP 2-NF interactions will also be examined with our monoclonal antibodies in normal neurons, experimentally induced NF aggregates and Alzheimer NFT by immunoelectron microscopy using the colloidal gold technique. We believe the proposed studies focus on a specific, potentially important and little studied neuronal protein that appears to have a role in the organization of the neuronal cytoskeleton in health and disease.